One of the most dangerous and insidious classes of viruses that has enormous economic impact in terms of health care costs and associated burdens is the Flaviviridae which include the well know hepatitis C virus (HCV) which cause significant health problems world-wide, as well as other viruses such as West Nile Virus (WNV) and Dengue or Yellow Fever virus which can be deadly with the potential for catastrophic epidemics.
The Flaviviridae are characterized as being positive sense single stranded RNA viruses that have a genome of about 10 Kb that generally encodes one long ORF composed of a number of genes that are transcribed as a large polyprotein. The large polyprotein is processed to yield different enzymatic and structural proteins which go on to assist in RNA replication and viral propagation with the assistance of host cell factors. It is thought that the lifecycle of Flaviviridae does not go through replicative DNA intermediates.
Disease caused by hepatitis C virus is an enormous burden on the world's health systems. HCV is a major cause of liver disease throughout the world. It is estimated that upwards of 10,000 deaths per year are attributable to HCV in the United States. About four million people in the United States have antibodies to HCV. It is estimated that well over 150 million people worldwide are chronically infected with HCV. Chronic hepatitis C can cause hepatitis, cirrhosis, liver failure, and liver cancer (hepatocellular carcinoma). There are a variety of subtypes of HCV including at least 6 major genotypes and 50 subtypes. As with many other viruses, HCV is known to mutate quickly, and changes in the envelope protein may help the virus avoid the immune system of the host.
Efforts to combat HCV have been met with limited success. Vaccines and immunoglobulin products for preventing HCV have been in development but are not currently available. Given the rapidly mutating nature of the virus and the variety of variants of HCV, it is a daunting task and if possible, it will likely take a long time to develop such products for prevention of HCV infection. The only preventative strategies relate to the ability to stop transmission of the virus by screening blood supplies and educating the public regarding high-risk groups and behaviors.
Two treatments are available in the United States for those infected with HCV: monotherapy treatment with alpha interferon or combination therapy with alpha interferon and ribavirin. Combination therapy appears to be the most efficacious treatment and therefore is the treatment of choice in the United States.
Alpha interferon monotherapy can be effective in treating chronic HCV, but it is not effective against all HCV infections and there can be unwanted side effects associated with this treatment option. The other treatment option is a combination therapy with alpha interferon and ribavirin. Again, there are undesirable side effects associated with this combination therapy.
Despite years of intensive research aimed at developing treatments and prophylactic measures against HCV, there is a need for new improved treatments of HCV.
A new class of compounds for treating HCV targets the viral protease. Telaprevir, recently approved by the FDA, is the front runner in this category, with first in class blockbuster potential. Other advanced clinical programs include nucleoside and non-nucleoside polymerase inhibitors which target the viral RNA polymerase.
The mechanisms that viruses use to propagate themselves involves co-opting certain aspect of their host cell to enter, be transported to the correct location in the cell (e.g., nucleus) for replication or establishment of latency, depart an infected cell and are only beginning to be understood on a general level. One long standing difficult goal in antiviral research has been the search of host cell factors that can be target for treating and preventing viral infection.
A group of enzymes known as lysine methyl transferases and lysine demethylases are involved in histone lysine modifications. One particular human lysine demethylase enzyme called Lysine Specific Demethylase-1 (LSD1) was recently discovered (Shi et al. (2004) Cell 119:941) and shown to be involved in histone lysine methylation. LSD1 has a fair degree of structural similarity, and amino acid identity/homology to polyamine oxidases and monoamine oxidases, all of which (i.e., MAO-A, MAO-B and LSD1) are flavin dependent amine oxidases which catalyze the oxidation of nitrogen-hydrogen bonds and/or nitrogen-carbon bonds. Although the main target of LSD1 appears to be mono- and di-methylated histone lysines, specifically H3K4 and H3K9, there is evidence in the literature that LSD1 can demethylate methylated lysines on non-histone proteins like p53, E2F1, Dnmt1 and STAT3.
Several groups have reported LSD1 inhibitors in the literature. Sharma et al. recently reported a new series of urea and thiourea analogs based on an earlier series of polyamines which were shown to inhibit LSD1 and modulate histone methylation and gene expression in cells (J. Med. Chem. 2010 PMID: 20568780 [PubMed—as supplied by publisher]). Sharma et al. note that “To date, only a few existing compounds have been shown to inhibit LSD1.” Some efforts were made to make analogs of the histone peptide that is methylated by the enzyme, other efforts have focused on more small molecule like molecules based on known MAO inhibitors. Gooden et al. reported trans-2-arylcyclopropylamine analogues that inhibit LSD1 with Ki values in the range of 188-566 micromolar (Gooden et al. ((2008) Bioorg. Med. Chem. Let. 18:3047-3051)). Most of these compounds were more potent against MAO-A as compared to MAO-B. Ueda et al. ((2009) J. Am. Chem Soc. 131(48):17536-17537) reported cyclopropylamine analogs selective for LSD1 over MAO-A and MAO-B that were designed based on reported X-ray crystal structures of these enzymes with a phenylcyclopropylamine-FAD adduct and a FAD-N-propargyl lysine peptide. The reported IC50 values for phenylcyclopropylamine were about 32 micromolar for LSD1 whereas as compounds 1 and 2 had values of 2.5 and 1.9 micromolar respectively.
Importantly, studies have also been conducted on amine oxidase inhibitor compounds to determine selectivity for MAO-A versus MAO-B since MAO-A inhibitors can cause dangerous side-effects (see e.g., Yoshida et al. (2004) Bioorg. Med. Chem. 12(10):2645-2652; Hruschka et al. (2008) Biorg Med Chem. (16):7148-7166; Folks et al. (1983) J. Clin. Psychopharmacol. (3)249; and Youdim et al. (1983) Mod. Probl. Pharmacopsychiatry (19):63).
Currently the treatments available for HCV and related diseases have serious drawbacks. There is a need for new drugs for these diseases that target novel points of intervention in the disease processes and avoid side-effects associated with certain targets. The invention described herein below provides an entirely new class of HCV antivirals.